Some cancers and neoplasms are easier to treat with radiation than others. Hard-to-reach neoplasms, such as those in the esophagus, intestines and other lumens, are often treated via Brachytherapy so as to minimize radiation to adjacent, healthy tissue.
Brachytherapy delivers radiation to small tissue volumes while limiting exposure of healthy tissue. In this regard, the delivered radiation conforms more to the target than any other form of radiation, (including proton therapy) as less normal transient tissue is treated. It features placement of radiation sources, such as small radioactive particles or needles, near or within the target tissue, thus having the advantage over External Beam Radiation Therapy (EBRT) of being more focalized and less damaging to surrounding healthy tissue.
Brachytherapy is a common treatment for esophageal, prostate, and other cancers. Approximately 15,000 and 480,000 cases of esophageal cancer are diagnosed in the U.S. and worldwide, respectively. At least 50 percent fail locally who present with curable cancers, which is to say that 50 percent suffer from persistence or recurrence of the cancers at the original cancer site.
Brachytherapy can be delivered in several rates: a Low-Dose Rate (LDR), a High-Dose Rate (HDR), and a very Low Dose Rate vLDR. The rates are expressed in Grays (Gy)/hour which are SI units of energy absorbed from ionizing radiation, equal to the absorption of one joule of radiation energy by one kilogram of matter. Since the inception of brachytherapy at the beginning of the 20th century (i.e., soon after the discovery of radiation) delivery has been predominately LDR.
LDR brachytherapy typically delivers radiation at a rate of about 50 cGy/hr (i.e., 0.5 Gy/hr) while HDR typically delivers at a rate of 5 Gy/min. The instantaneous rate is much higher at each dwell location for HDR brachytherapy as a very active source must traverse the various treatment locations during each treatment.
LDR brachytherapy delivers radiation continuously, while HDR brachytherapy delivers radiation intermittently over several days. Regardless of the dose rate, a total final dosage of 60 Gy or less is usually delivered to the patient during brachytherapy if it is the sole source of radiotherapy, and a total dose of 20-40 Gy is delivered during brachytherapy when used in combination with other forms of radiation treatment. These scenarios involve temporary implants in which the device is removed after completion of treatment.
Brachytherapy has been used to treat prostate cancer which has been practiced for more than half century. In this situation, very low activity material emitting a low energy is placed next to or within a tumor. Until now these low emitting devices have mostly been left in place permanently except in extraordinary circumstances. The most commonly employed LDR source is Iodine-125 (125I) which decays at a low energy radiation of 30 keV and emits radiation at a dose rate of 0.4-1.0 Gy/hr (4 to 10 cGy/hr) for multiple days up to a nominal year. vLDR is commonly used for cancers in which the radiation source can be placed proximate to or in the neoplasm and left for a significant period of time or permanently, such as when radioactive material or seeds are placed in prostate tumors. vLDR sources are considered permanent implants but this invention provides an option for replacing the radioactive material while the physical carrier of the radiation source remains at the treatment site.
Clinicians administer HDR brachytherapy in multiple sessions to improve patient tolerance. Thus, the patient is subjected to the additional risk of multiple procedures, often requiring anesthesia. Patients with cancers within lumen, ducts, or tracts, such as cancer of the esophagus or biliary tract of the liver, have less tolerance for brachytherapy if connections (for example, catheters) are connected externally for multiple days, because of irritation and the risk of life-threatening infections.
HDR employs a primary housing containing a relatively high energy source (about 10 Ci), such as Iridium-192 (0.4 MeV). Treatment sessions last about 30 minutes. HDR is commonly applied in 2 to 3 daily sessions over the course of a few days, or multiple placement of an after-loading catheter in e.g. esophageal cancer treatment.
Brachytherapy dosage is usually calculated at a fixed distance from the radiation source. HDR requires a highly active source delivering radiation at a dose rate of about 12 to 20 Gy/hr. Hot and cold spots, due to uneven distribution of radiation does, occur with small deviations in distance between the tissue and the radiation source. Thus, brachytherapy treatment using a centralized radioactive material housing or containment can result in significant patient toxicity if the radioactive source is not centralized. For example, for patients with esophagus cancer, potentially life-threatening fistulas occurred at a rate of 12 percent when treated with HDR brachytherapy in the study of Gasper et al, International Journal of Radiation Oncology, Biology, Physics 38 (1) 127-321 (1997), the entirety of which is incorporated by reference. However, there are many reasons for the source to be skewed to one side as even an active tumor could displace the source. Lastly, HDR treatment requires a specially shielded patient room with appropriate radiation precautions.
State of the art devices for delivering radiation to internal tissues lack two important essential features: 1) the ability to remove or replace the radiation sources in situ when clinically appropriate, and 2) the ability to change the geometry, energy or radioactive sources of the radioactive particles or seeds in situ according to clinical needs. Typically, once the radiation source carrier and the radiation source is placed, they remain permanently within the patient. Leaving a permanent radiation source in a patient, where it or its carrier may migrate over time or the tumor may change in shape or size, has the undesirable effect that healthy tissue will be exposed to the radiation, while the target cancerous tissue is not. The ability to remove the radioactive sources in this situation or prior to surgery, while clinically useful, is currently lacking from the state of the art.
Additionally, it may be clinically necessary to continue radiation therapy after the activity of the radioactive material has decayed. For example, 125I has a half-life of about 60 days. If the tumor is still present or grows in size after an initial brachytherapy treatment (which sometimes occurs within six months), then it would be advantageous to replace the depleted radiation source with a source that has higher activity or shorter half-life. This is because faster growing tumors may be better controlled with radiation that has a shorter half-life or that decays and emits radiation faster.
Additionally, it would be advantageous to adjust the position and the activity of the radioactive source on its carrier in response to changes in tumor shape and size, carrier position, and other relevant therapeutic factors. It also may be appropriate to remove the radiation sources before surgery or other intervention to reduce personnel exposure or damage to sensitive equipment.
A need exists in the art for a device to deliver radiation and other medicaments to a patient at a lower total but more concentrated dose but with the beneficial effects of a higher dose. The device should facilitate the removable positioning of vLDR radiation sources in close spatial relation to the neoplasm or target tissue requiring treatment. The device should therefore feature a means for accommodating indefinite placement of the radiation source proximal to the target tissue, the means also allowing for removal or replacement of the radiation source, all with minimal invasive activity. The device should also allow the radioactive sources to be positioned in a preformed geometry that is customized to patient anatomy and the target tissue.